1. Field of the Invention
The present invention relates to input stages for monolithically integrated charge transfer devices, and in particular input stages for such devices which generate to complementary charge packets from a single input signal.
2. Description of the Prior Art
An input stage for a monolithically integrated charge transfer device which generates a pair of complementary charge packets from a single input signal is known, for example, from the article "A Symmetrical Balanced Linear Differential Charge-Splitting Input for Charge-Coupled Devices", IEEE Transactions on Electron Devices, Vol. ED-24, No. 6, June, 1977 at pages 746 through 750. As described therein, the input stage has two adjacent input gate electrodes which are connected to voltages of different magnitudes, which magnitudes differ from one another by the amount of an input signal. A strip-like dividing gate is disposed between the input gate electrodes. Charge packets of constant size derived from a source region in a semiconductor body are shifted by transfer gate electrodes into the semiconductor zone beneath the two input gate electrodes, at which point the charge packets are divided into two complimentary charge packets as a result of the potential wells formed beneath the input gate electrodes according to the different voltages supplied thereto. After this division, a voltage is supplied to the dividing gate between the input gate electrodes such that a potential barrier arises between the electrodes. The complimentary charge packets are then shifted electrode-by-electrode in two separate transfer channels of the charge transfer device in the direction toward the output stage.
The disadvantage of the above-described structure is the relatively large area of semiconductor surface which is required by the two input gate electrodes and the two transfer channels. Moreover, different electron trap concentrations at the semiconductor boundary surface may exist in the two transfer channels, so that the two complimentary charge packets are subjected to different thermal influences during transfer thereof and are thereby distorted to different degrees in the separate channels.
The theory and operation of basic charge transfer devices of the type which may be utilized in the present invention in combination with the improvements disclosed herein are known, for example, from the text "Charge Transfer Devices", Sequin and Tompsett, Academic Press, New York, 1975 at pages 1-18 and 52-56. Output stages for such devices of the type known as "floating diffusion outputs" and "floating gate outputs" which may be utilized in the present invention are described in detail in the article "Charge Coupled Devices-An Overview", W. F. Kosonocki, WESCON Technical Papers, 1974, Vol. 18, at page 7 of section 2/1.